Cannot connect Telnet x.x.x.x SMTP

Hi All, i had several domains (Domain1-4) hosted on one server (Server1) and all sent/received emails efficiently to one another and remote. I have recently removed one domain (Domain4) to its own server (Server2). Since then, the other domains (Domain1-3) cannot send mail to Domain 4 on Sever2. Is there a file of files that may still contain references to Domain4 on Server1. If so, could you point me in the right direction. I am competent to delve into the system.

I can sucessfully resolve the MX record from Domain1-3 to Domain4
I can successfully traceroute to from Server1 to Server2
1 can suceesfully telnet SMTP from Server2 to remote Domains
I can suceesfully telnet SMTP from Server1 remote Domains
I can suceesfully telnet SMTP from Server2 to Server1
I cannot telnet SMTP from Server1 to Server2